Cancer is an abnormality in a cell's internal regulatory mechanisms that results in uncontrolled growth and reproduction of the cell. Normal cells make up tissues, and when these cells lose their ability to behave as a specified, controlled, and coordinated unit, (termed “dedifferentiation”), the defect leads to disarray among the cell population. When this occurs, a tumor begins to propagate.
In addressing a cancerous condition, the essence of many medical treatments and procedures involves the removal or destruction of the tumor tissue. Examples of significant types of treatments include the surgical removal of cancerous growths and the destruction of metastatic tumors through chemotherapy and/or radiation therapy.
Surgery often is the first step in the treatment of cancer. The objective of surgery varies. Sometimes it is used to remove as much of the evident cancerous tumor as possible, or at least to “debulk” it (remove the major bulk(s) of tumor so that there is less that needs to be treated by other techniques). Depending on the type of cancer and its location, surgery can also provide some symptomatic relief to the patient. For example, if a surgeon can remove a large portion of an expanding brain tumor, the pressure inside the skull will decrease, leading to improvement in the patient's symptoms.
However, not all tumors are amenable to surgery. Some may be located in parts of the body that render them impossible to completely excise. Examples of these would include tumors in the brainstem (a part of the brain that controls breathing) or a tumor which has grown in and around a major blood vessel. In these cases, the role of surgery is limited due to the high risk associated with tumor removal.
In some cases, surgery is not employed to debulk a tumor because it is simply not necessary. An example is Hodgkin's lymphoma, a cancer of the lymph nodes that responds very well to combinations of chemotherapy and radiation therapy. In Hodgkin's lymphoma, surgery is rarely needed to achieve cure, but almost always used to establish a diagnosis (i.e. in the form of a biopsy).
Chemotherapy is another common form of cancer treatment. Essentially, it involves the use of medications (usually administered orally or by injection) which specifically attack rapidly dividing cells (such as those found in a tumor) throughout the body. This makes chemotherapy useful in treating cancers that have already metastasized, as well as tumors that have a high chance of spreading through the blood and lymphatic systems but are not evident beyond the primary tumor. Chemotherapy may also be used to enhance the response of localized tumors to surgery and radiation therapy. This is the case, for example, for some cancers of the head and neck.
Unfortunately, other cells in the human body that also normally divide rapidly (such as the lining of the stomach and hair) also are affected by chemotherapy. For this reason, many chemotherapy agents induce undesirable side effects such as nausea, vomiting, anemia, hair loss or other symptoms. These side effects are temporary, and there exist medications that can help alleviate many of these side effects. As knowledge in the medical arts has continued to grow, researchers have devised newer chemotherapeutic agents that are not only better at killing cancer cells, but that also result in fewer side effects for the patient.
As also discussed generally above, radiation therapy is another commonly used weapon in the fight against cancer. Ionizing radiation kills cancer by penetrating skin and intervening tissue, and damaging the DNA within the tumor cells. The radiation is delivered in different ways. The most common delivery technique involves directing a beam of radiation at the patient in a highly precise manner, focusing on the tumor. In performing this treatment, a patient lies on a table and the beam source moves around him or her, while transmitting the therapeutic radiation dose in a directed manner. The procedure lasts minutes, but may be performed daily for several weeks (depending on the type of tumor), to achieve a particular total prescribed dose. A radioisotope can be safely used to deliver local radiation for cancer treatment. A typical example of a radioisotope is I-131 for the treatment of thyroid cancer.
Another radiation method sometimes employed, called brachytherapy, involves implanting radioactive pellets (seeds) or wires in the patient's body in the region of the tumor. The implants can be temporary or permanent. For permanent implants, the radiation in the seeds decays over a period of days or weeks so that the patient is not rendered radioactive. For temporary implants, the entire dose of radiation is usually delivered in a few days, and the patient must remain in the hospital during that time, due to the need for observation and generally in view of his or her heightened radioactivity. For both types of brachytherapy, radiation is generally delivered to a very targeted area to gain local control over a cancer (as opposed to treating the whole body, as is accomplished using chemotherapy).
A number of other cancer therapies exist, although presently, the majority of such treatments are under exploration in clinical trials, and have not yet become a standard of care. Examples of such varied treatments include the use of immunotherapy, monoclonal antibodies, anti-angiogenesis factors and gene therapy. A brief description of each of these relatively new treatment regimes is as follows:
Immunotherapy: There are various techniques designed to assist the patient's own immune system fight the cancer, quite separately from radiation or chemotherapy. Oftentimes, to achieve the goal, researchers inject the patient with a specially derived vaccine that strengthens the particular immune response needed to resist the cancer.
Monoclonal Antibodies: These are antibodies designed to attach to cancerous cells (but not normal cells) by taking advantage of differences between cancerous and non-cancerous cells in their antigenic and/or other characteristics. The antibodies can be administered to the patient alone or conjugated to various cytotoxic compounds or in radioactive form, such that the antibody preferentially targets the cancerous cells, thereby delivering the toxic agent or radioactivity to the desired cells.
Anti-Angiogenesis Factors: As cancer cells rapidly divide and tumors grow, they can soon outgrow their blood supply. To compensate for this, some tumors secrete a substance believed to help induce the growth of blood vessels in their vicinity, thus providing the cancer cells with a vascular source of nutrients. Experimental therapies have been designed to arrest the growth of blood vessels to tumors, thereby depriving them of needed sustenance.
Gene Therapy: Cancer is the product of a series of mutations that ultimately lead to the production of a cancer cell and its excessive proliferation. Cancers can be treated by introducing genes to the cancer cells that will act either to check or stop the cancer's proliferation, turn on the cell's programmed cell mechanisms to destroy the cell, enhance immune recognition of the cell, or express a pro-drug that converts to a toxic metabolite or a cytokine that inhibits tumor growth.
Another option for treatment in certain types of cancers is to employ an isotope that is tailored to be taken-up by the particular organ or tissue. For example, Iodine 131 is employed to treat thyroid cancer. The thyroid cancer cells have hundreds more times the potential to attract in the radioactive Iodine I-131 than other cells. The Iodine isotope effectively kills cancer cells in the thyroid. Advantageously, the radioactive wave of I-131 does not travel far, so it does not kill the cells of other organs than thyroid tissue. This renders the administration of Iodine a safe treatment in thyroid cancer and over active thyroid disease, and it has been used in this context for decades. However, the use of a “raw” isotope is only applicable to organs and tissues that have an affinity for the underlying element. In general, most organs and tissues do not selectively uptake a particular element having a radioactive, yet short-distance-acting, isotope.
It is therefore desirable to provide a compound/agent and treatment method employing such a compound/agent, which destroys, and hence either facilitates the removal of or inhibits the further growth of tumor cells and tissue, while exhibiting mainly local effects and minimal or no systemic toxicity. This compound and treatment method should accomplish its goals in a manner that is free of significant damage to non-cancerous cells and that is highly selective for cancer cells. The compound and treatment method should also potentially be applicable to a wide variety of organs and tissues.